This invention relates in general to tapered roller bearings and more particularly to molded polymer cages for such bearings.
The typical cage for maintaining the proper spacing between the rollers of a tapered roller bearing is a metal stamping having pockets in which the rollers are received. To be more specific, the cage has a small end ring that extends across the small end faces of the tapered rollers, a large end ring that extends across the large end faces of the rollers, and bridges that connect the two rings and actually separate the rollers. Not only does the cage maintain the correct spacing between the rollers, but it further serves to retain the rollers about the cone or inner race. In other words, it unites the cone, the rollers, and of course the cage into a cone assembly which remains intact when removed from the cup or outer race. To this end, the typical stamped metal cage is located beyond the pitch circle, that is beyond the axes of rotation for the individual rollers, and further has the side planar edges of its bridges beveled to conform tangentially to the contour of the adjacent sides of the rollers. Indeed, stamped metal cages have substantial roller retaining capabilities which serve the bearing well during assembly and maintenance procedures when the cone assembly must be handled apart from the cup.
While the typical metal cage has excellent retention characteristics, it is expensive to produce and install in that the steel has relatively little flexibility or elasticity. These limitations require installation of the cage on the cone with the cage bridges spread, that is somewhat bowed, for otherwise the cage will not pass over the rollers that are about the cone. Once the cage and rollers are around the cone, the bridges are straightened in a press operation. This requires very specialized equipment. The absence of significant elastic movement for steel also imposes design limitations.
To simplify assembly and increase design options, some bearing manufacturers have employed cages molded from suitable polymer resins. These cages are not only less expensive in their own right, but they are also more easily installed due to their flexibility. However, to provide adequate strength and roller retention, polymer cages heretofore developed have been quite large, their bridges often exceeding one-half the diameter of the rollers. As a result, these cages require a considerable amount of polymer resin to manufacture. Moreover, the large surface areas that these bridges present toward the rollers increase the contact forces between the rollers and cages and leave less free space for lubricant, both of which are undesirable.